The horizontal-axis wind turbines used in a conventional wind turbine has a plurality of blades (three blades in many cases), the pitch angles of which are changed according to the wind speed so as to change the rotational speed of the rotor and thereby to control the energy efficiency of the blades. The wind turbine has a pitch controller, turbine controller, and power supply facility as a mechanism for changing the pitch angles of the blades. The turbine controller creates a pitch angle command according to the wind speed measurement obtained by an anemometer, the rotational speed detected by a rotational speed detector, and the quantities of the operation mode and other states of the wind turbine. The turbine controller then sends the created pitch angle command to the pitch control unit. The auxiliary equipment has an uninterruptible power supply for supplying power to the pitch controller and turbine controller if the system voltage drops due to a grid failure, thereby enabling pitch angle control to be continued according to a command from the turbine controller even during the grid failure. The above technology is described in, for example, WO 2004/067958.